They 'flushed' impurities from the system. = They 'flushed' impurities out of the system.
She published her first novel while still 'in the flush of' youth. [=while still young]
The committee succeeded in 'flushing out' [='finding'] several good candidates.
(..) Uh, are you done in there? ( squeals ) Ah! Sorry. Sorry. ( singing ) ( toilet flushes ) Okay, you finished now, right? Hello? ( yells ) Boo. (..)2001 Monsters, Inc.